History
Historically, DRAMs have had relatively large memory cells with large supply voltages. Over the last two decades, the densities of DRAM's has doubled on the average of every year and a half. This rapid increase in bit density is the result of intensive technical efforts by design and process engineers. However, several problems have been created by making smaller and denser DRAMs.
Detection of small voltage signals can be a problem in DRAMs. There are several causes: First, the dynamic sense amplifier circuit is not accurately fabricated in complete balance. Second, the memory array produces a noise which disturbs the small signal detection. Third, the peripheral circuits, such as timing pulse generators, work as a kind of noise source on the sensing circuit. Forth, the stored charge in a memory cell gets so small in a five or less volt device, that it is difficult to sense the digital ones signal. This invention will focus on improving the last problem.